Carburetor

ABSTRACT

Automatic choke for primary and secondary carburetor barrels of gasoline engine has temperature-responsive means connected to primary choke plate and to secondary choke plate, connection to primary plate being yieldable to permit primary plate to be moved toward open position by intake suction and/or intake air flow while secondary choke plate stays closed. When power operation is needed during choked condition, secondary throttle opens giving proper choked operation of secondary barrel which can also have intake suction and/or intake air flow arrangements for moving secondary choke plate toward open condition. Automatic choke can have temperature-adjusted control for variably limiting opening of choke by intake suction and thus provide better performance. Primary induction passage preferably has small cross-sectional area (not more than one-eighth of the total cross-sectional area of all induction passages), and idling desirably arranged to take place on the main jet.

United States Patent 191 Marsee 1 Jan. 15, 1974 Related US. Application Data [63] Continuation-in-part of Ser. No. 812,519, Feb. 25, 1969, abandoned, which is a continuation-in-part of Ser. No. 700,321, Jan. 3, 1968, abandoned, which is a continuation-impart of Ser. No. 551,463, May 19, 1966, abandoned.

[75] Inventor:

[52] US. Cl. 261/23 A, 261/39 B, 261/52 [51] 1 Int. Cl. F02m U111 [58] Field of Search 261/39 B, 23 A, 52; 123/119 F, 127

[56] References Cited UNITED STATES PATENTS 1122,968 1/1948 Stanton 261/39 13 X 2,095,746 10/1937 Jacobs 123/103 2,942,596 6/1960 Carlson 123/119 3,171,395 3/1965 Bartholomew 123/127 3,282,261 11/1966 Bartholomew 123/119 3,294,374 12/1966 Smith et al 261/23 3,310,045 3/1967 Bartholomew 123/127 [5 7] ABSTRACT Automatic choke for primary and secondary carburetor barrels of gasoline engine has temperatureresponsive means connected to primary choke plate and to secondary choke plate, connection to primary. plate being yieldable to permit primary plate to be moved toward open position by intake suction and/or intake air flow while secondary choke plate stays closed. When power operation is needed during choked condition, secondary throttle opens giving proper choked operation of secondary barrel which can also have intake suction and/or intake air flow arrangements for moving secondary choke plate toward open condition. Automatic choke can have temperature-adjusted control for variably limiting opening of choke by intake suction and thus provide better performance. Primary induction passage preferably has small cross-sectional area (not more than one-eighth of the total cross-sectional area of all induction passages), and idling desirably arranged to take place on the main jet.

14 Claims, 7 Drawing Figures PATENTED 1 51974 3. 785.824

' sum 3 or 3 1e; v m 75 CARBURETOR CROSS REFERENCE TO RELATED APPLICATIONS The present application is a continuation-in-part of application Ser. No. 812,519, filed Feb. 25, 1969 and subsequently abandoned, which in turn is a continuation-in-part of application Ser. No. 700,321, filed Jan. 3, 1968, now abandoned, which in turn is a continuation-in-part of application Ser. No. 55 L463, filed May 19, I966, now abandoned.

Among the objects of the present invention is the provision of carburetor systems that give low exhaust emission and have an automatic choke enabling improved operation.

In accordance with this invention, a carburetor has a primary barrel and a secondary barrel to supply a fuel mixture to an internal combustion engine, the primary barrel being arranged to operate the engine on a fuelair mixture which is relatively lean so that the engine s exhaust contains very little carbon monoxide and unburnt or partially burnt hydrocarbons. The primary barrel has a relatively small cross-sectional area, causing its mixture to move through at relatively high speed. This is an important factor in reducing undesired exhaust emissions when the engine is operating on only the primary barrel. A primary choke plate is provided for the primary barrel for movement between open and choked positions, and a secondary plate is likewise provided for the secondary barrel. A temperatureresponsive device moves both choke plates to their choking positions when the engine temperature is below a predetermined minimum and opens the plates when the temperature is above the minimum. Yieldable means is provided in the connection of the temperature-responsive device which allows the primary choke to be moved toward opened position while the temperature-responsive device holds the secondary plate in less open position.

A suction cylinder can be connected to the primary choke plate to open it without opening the secondary plate when the engine requires additional air for the fuel mixture, and its temperature is below the predetermined minimum. A second suction cylinder may be I connected to open the secondary choke plate when the engine is cold and is operated at high speed and light load.

The secondary choke plates require a higher torque to hold them in their choked positions than the torque required to hold the primary choke plates since the air load acting upon them is greater than the load which acts upon the primary plates. The torque necessary to hold the secondary choke plates must be sufficient so that an increased air load during acceleration does not pull them open and thereby cause a lean acceleration and possible backfiring of the engine. Thus, the components of the automatic choke of this invention are constructed and arranged so that the force of the suction cylinder connected to open the primary choke plate is sufficient to overcome the influence of the yieldable means and open the plate. Such an arrangement enables the temperature-responsive device to move the primary and secondary choke plates to their choked positions and also allows the primary plate to be opened by its associated piston while the temperatureresponsive device maintains the secondary choke plate in less opened position.

The suction cylinders can have temperatureresponsive elements connected to gradually reduce the maximum choke opening they provide, as the choking temperature decreases. This particularly improves operation when the carburetor is adjusted to give an unchoked combustion mixture having an air-fuel weight ratio of at least about 14.5 to l. A ratio of 15 to 1 makes a highly desirable combustion misture inasmuch as it produces an exhaust with a very low content of combustibles, and this mixture is readily used at low and medium. power road loads particularly with a primary induction system that has a cross-sectional area about one-tenth to one-fifth that of the cross-sectional.

area of the entire induction system. Such a primary system generally has a venturi with a cross-sectional area of one-eighth to one-fifth square inches per cubic inches of total piston displacement of the engine operated with the carburetor.

To make use of the leanest possible fuel mixture, it is particularly helpful to have the carburetor arranged so that idling is carried out on the main jet. This type of arrangement in which a venturi jet supplies all idle fuel as well as fuel for all other modes of engine operation is described in U. S. Pat. No. 3,310,045 granted Mar. 21, 1967, and provides a very uniform combustion mixture over all speed ranges so that there is no need for the enrichment generally resorted to to bridge the shift-over of fuel from an idle jet to a main jet.

Novel combinations and advantages of the present invention will become apparent to one skilled in the art from the following description in conjunction with the accompanying drawings wherein similar reference characters refer to similar parts and in which:

FIG. 1 is an elevational view partly in section of an embodiment of the present invention with the induction passages of a multibarrel carburetor shown in phantom outline;

FIGS. 2, 3, 4 (considered along with 4A) and 5 are similar views of other embodiments of the present invention; and

FIG. 6 is an elevational view parly in section of a single barrel carburetor embodiment of the present invention.

Referring in more particularity to the drawings, numeral 10 represents a multibarrel carburetor having at least one primary induction passage 12 and at least one larger secondary induction passage 14. A primary choke plate 16 movable between opened and choked positions is mounted in the primary induction passage by a pivot pin 18 extending through the side walls defining the passage. A larger choke plate 20 conforming generally to the cross-section of the secondary induction passage is similarly journaled in the secondary passage for movement between opened and choked positions. The choke plates are unsymmetrically mounted in their respective induction passages so that air moving into the carburetor urges each plate toward open position, as explained more fully below. The carburetor 10 further includes a primary throttle plate 22 suitably journaled in the primary induction passage by a pivot pin 24. The throttle plate is connected to a throttle pedal (not shown) by a link 26 secured to one end of the pivotpin 24 and a rod 28 fastened to the pedal.

A fast idle cam 30 mounted for pivotal movement upon the carburetor is provided to prop the primary throttle plate 22 open when the internal combustion engine upon which the carburetor is mounted is below a predetermined minimum temperature, such as 72 F. The cam has a series of steps 32, 34, 36 which cooperate with a fast idle adjusting screw or tang 38 connected to the primary throttle plate 22 by an L-shaped lever 40. The position of the cam relative to the tang controls the opening of the throttle plate within the primary induction passage when the engine is idling, as explained below.

A temperature-responsive device such as a bimetallic spring 42 constructed of two dissimilar metals having different coefficients of expansion is connected to the primary and secondary choke plates to move them to their choked positions when the engine temperature is below the predetermined minimum. The bi-metallic spring 42 may be secured directly to the secondary choke plate to move it to its choked position or to an L-shaped lever 44 pivotally mounted upon the carburetor by a pin 46. One end of the spring 42 may be connected to the pivot pin 46 and the other to the outer end of the lever arm 48.

The lever is connected to the secondary choke plate 20 by a rod 50 and a link 52 secured to the secondary plate so that the temperature-responsive device causes the choke plate to move to its choked position when the temperature is below the predetermined minimum. The L-shaped lever 44 is also connected to the primary choke plate 16 by a sectional rod 54 and the arm 56 of an L-shapcd lever 58 secured to the pivot pin 18 of the primary choke plate. The rod 54 includes an upper section 60 pivoted to the lever 58 and a lower section 62 pivoted to the lever 44. Biasing means such as a capsulated spring 64 is suitably mounted between the upper and lower sections of the rod 54 to enable them to move toward and away from each other to thereby vary the overall length of the rod 54, as explained more fully below.

The primary choke plate is connected to the fast idle cam 30 by a link 66 fastened to an end of the pivot pin 18 and a rod 68 pivoted to the link. The rod includes a terminal offset portion 70 slidably disposed within an arcuate slot 72 in the cam to control the rotation of the cam about its pivot.

Lever 58 is also secured by a piston rod 74 to a primary suction cylinder 75 connected to the intake manifold of the engine by a line 76. The piston rod holds the primary choke plate open during light throttle, high manifold vacuum operation since under these conditions air flow alone may be insufficient to open the choke plate enough for smooth engine performance. A second cylinder (85 in FIG. 3) may similarly be pro vided to open the secondary choke plate when the engine temperature is below the predetermined minimum, to give good high load performance during warm-up. However, air flow alone through the secondary induction passage can be relied on to open the secondary choke plate, as in FIG. 1.

The carburetor also includes fuel nozzles 78 and 80 disposed within the venturis of the induction passages 12 and 14, respectively. Additionally, the secondary induction passage 14 has a throttle plate 82 suitably journaled therein adapted to be opened when the engine requires additional fuel mixture. Where a secondary suction cylinder is used it can be operated by the air pressure upstream of the secondary throttle so that i the secondary cylinder opens the secondary choke only when the secondary throttle is opened.

In operation the construction of FIG. 1 functions to accurately supply a fuel mixture including choked modes, to a V-8 internal combustion engine having two secondary carburetor barrels and one or two primary carburetor barrels. When the engine temperature is below a predetermined minimum value such as 72 F and the throttle pedal has been depressed and then released, the various components are positioned as illustrated in FIG. 1. Both the primary choke plate 16 and the secondary choke plates 20 are held in their choked positions by the temperature-responsive device 42 acting through the sectional rod 54 and the rod 50. When the engine begins to fire regularly the manifold vacuum increases thereby causing the primary piston 74 to partially open the primary choke plate. This arrangement provides adequate fuel for easy starting in cold weather without making the mixture overly rich when the engine is operating with high manifold vacuum. When the throttle is opened manifold vacuum diminishes and the piston exerts less opening force on the primary choke and plate. However the increased air flow resulting from the larger throttle opening acts upon the offset primary choke plate to open it the desired amount. A yieldable or one-way connection like a spring (not shown in detail) between the choke plate 16 and its pivot pin 18 permits such opening.

The arrangement of the moving elements permits the suction cylinder to open the primary choke plate without opening the secondary since only the upper portion 60 of the sectional rod 54 moves against the influence of the capsulated spring 64, when the primary plate is so opened. The force of the piston must only be sufficient to overcome the spring 64 in order to open the primary choke plate.

When considerable power is desired and the engine is still cold, the secondary throttles open so that air can flow into the secondary carburetor throats. Although such air flow is usually sufficient to open the secondary plates in the same way as in the primary induction passage, the second vacuum cylinder 85 may be provided to help open it in the same way that the primary vacuum cylinder helps open the primary choke plate. Unlike the primary piston, the force of the secondary piston must be sufficient to overcome the force of the temperature-responsive device 42 to open the secondary choke plates if those plates are rigidly connected to the device 42. In the event the engine temperature is still below the minimum value when the power requirement is reduced, both the primary and secondary plates return to choking positions.

As the engine continues to run its temperature continues to increase and when it finally reaches the predetermined minimum value, the temperature-responsive device causes each of the choke plates to open. With the primary choke plate open, the offset portion 70 of the rod 68 is free to slide downwardly in the arcuate slot 72 of the fast idle cam 70. This permits the cam to drop so that the idle adjusting screw 38 moves from step 36 to 34 thereby reducing the idle of the engine. Continued warm-up of the engine causes the choke plates to open even farther and the offset portion 70 continues its downward travel in the slot/72. This movement permits the cam to drop farther and the adjusting screw 28 to move from step '34 to 32 thereby further reducing the idle of the engine; I

When the engine temperature is sufficiently above the predetermined minimum, both the primary and secondary choke plates are in full open position and the screw 38 is in contact with the step 32 of the fast idle cam 30. The choke plates remain in open position until the engine temperature drops below the predetermined value. The temperature-responsive device 42 then cuses the secondary choke plates to move to choked position, but the primary plate is prevented from moving by the rod 68 which holds it in open position. Under these circumstances the capsulated spring 64 is slightly compressed and when the throttle pedal is depressed, thereby moving the adjusting screw 38 away from the fast idle cam 30, the cam and the rod 68 are free to move upwardly under the influence of the spring to close the primary choke plate. When the throttle pedal is released, the idle adjusting screw 38 engages the step 36 of the cam to thereby position the throttle plate 22 in its most open idling position.

FIG. 2 illustrates another embodiment of the present invention which may be substantially similar to the embodiment shown in FIG. 1 except for the modified lever 84 and link 86. A hairpin spring mounted upon the lever 84 is connected to engage an offset portion 90 of link 86 to urge the rod upwardly. When the primary and secondary choke plates are in their choked positions and the piston rod 74 together with the air flowing through the primary induction passage acts upon the primary plate to open it, the terminal portion 90 of the link 86 slides downwardly in an arcuate slot 92 in the lever against the influence of the spring 88. This causes the primary choke plate to open without opening the secondary plate, in the same manneras the arrangement illustrated in FIG. 1.

For convenience and clarity, only two induction passages of a multibarrel carburetor have been illustrated. Although the arrangement of the instant invention may be utilized to choke a two-barrel compound carburetor of the illustrated type, it is readily employed to control the flow of air through additional passages. For example, when the carburetor includes two or more secondary induction passages, the rod 50 may be modified so that each secondary choke plate is moved to choking position by the temperature-responsive device. Two

primary choke plates may also be connected to the temperature-responsive devicein the same manner as the primary plate 16. Thus, a single temperatureresponsive device is utilized to control the flow of air through any desired number of induction passages.

By having only one primary induction passage in a multibarrel carburetor system, making that passage of extremely small cross-sectional area in comparison to the primary passages of the more popular carburetors, and by providing each primary and secondary passage with a choke plate, the emission of combustibles through the exhaust system is significantly reduced without limiting the performance of an automobile powered by an engine having such an induction system. Also the fuel economy of such an engine is considerably better than is now conventional. A preferred primary passage size is such that its cross-sectional area is not more than about one-eighth of the total induction passage cross-section, although good results are obtained with the fractions between one-tenth and onefifth.

The construction of FIG. 4 is a particularly desirable embodiment of the present invention. It incorporates.

all the features of the construction of FIG. 1 and in addition a variable limit stop for the amount of primary choke opening effected by suction cylinder 75. For this purpose piston rod 74 carries an arm 94 that is limited in its choke-opening travel by engagement with a tapered limit slide 96. The slide is shown as having a slot 95 by which it is guided for vertical sliding movement on a fix pin 97. An extension 98 for the slide is pivotally connected to an arm 93 fixed to the spring-holding pin 46 but rotatable with that pin under the influence of the thermally-responsive spring 42. A bias spring 92 which is not thermally responsive is shown as a simple coil looped around pin 46 with ends projecting out and compressed between arm 93 and a fixed lug 91. A stop can also be used to limit the upward travel of arm 93, if it is not desired to use the pin-and-slot combination 97, 95 for such limiting. As so arranged movement of the choke spring 42 will raise and lower the slide 96 in addition to effecting actuation of the choke valves 16, 20. The foregoing arrangement is more fully illustrated in the partly broken-away perspective view of FIG. 4A.

The construction of FIG. 4 is illustrated in maximum cold condition with both choke valves closed and the slide lowered to minimum height. Upon starting of the engine with the carburetion system in this condition, regular firing will develop sufficient intake manifold suction to actuate cylinder 75 and bring its piston rod 74 over to the left the relatively short distance permitted by slide 96. This opens primary choke valve 16 a relatively small amount as needed to keep the engine running under very cold conditions. As the engine warms up, choke spring 42 unwinds, gradually retracting its operating rods 50 and 62 and also permitting extension 98 to be elevated by bias spring 92. This permits piston rod 74 to move a little farther to the left, allowing primary choke valve 16 to open a little farther. This reduces the degree of choking at low engine speed such as at fast-idle operation in comparison with very cold operation and in conformity with the amount of choke required as operating temperatures vary.

Similarly when the engine is first started under conditions that are not quite as cold as illustrated in FIG. 4, the slide 96 will be in a higher position and the suction cylinder 75 will open the primary choke valve more than it would under colder conditions. The entire operation of the contruction of FIG. 4 can accordingly be effected with minimum choke enrichment under all op erating conditions of the engine and with minimum emission of combustibles from the exhaust.

The above type of operation is even further refined by arranging for the primary induction passage 12 to operate without a separate idle jet, the idling being effected on the main jet as described in U. S. Pat. No. 3,310,045. As explained in that patent, passage 12 is made of a relatively small cross-sectional area such as about one-eighth of the cross-sectional area of the entire induction system, and about 0.16 square inches for every cubic inch of total piston displacement in the engine. The maximum air flow rate through the primary passage is then about 10 to 15 times the minimum air flow rate through that passage, enabling the engine to idle on the main jet alone.

i In the foregoing combination the primary induction passage 12 can be arranged toprovide an unchoked combustion mixture having an air fuelratio of at least 14.5 to .l, preferably 15 -to l. This-combined with the minimum choking obtained at all choking temperatures because of the uniform variable suction opening limit, provides an engine operation that readily passes all 1966 emission requirements even without a second suction cylinder to open the secondary choke 20, as in FIG. 3. Such a second cylinder can also be provided in the construction of FIG. 4, if desired.

The gradually varying stop feature for the suction cylinder 75 is also very helpful in reducing the choking of engines whether or not the engines are operating with applicants very lean mixture and whether or not the engines have a secondary induction passage. Also while the varying suction cylinder stop is shown in FIG. 4 as actuated by the same temperature-responsive member which also actuates the choke valves, a separate temperature-responsive member can be used for the suction cylinder stop if desired.

FIG. shows such a separate temperature-responsive member used with a modified arrangement for providing a continuously variable degree of choke-valve opening at low engine speed. In this construction a suction head 101 of the diaphragm type is used in place of the cylinder to operate control rod 74. The suction suply line 103 to the diaphragm connected through a control box 105 to a manifold tap 107. Control box 105 with a bleed'or vent orifice 124 in the wall has a yieldable diaphragm wall 109 that carries a modulating pin 111 with a tapered point 113 closely adjacent a seat 115 to control the size of the opening through which suction is applied from manifold tap 107 to suction line 103. A J-shaped bimetallic spring 117 has its short arm secured to the rim of the box, as indicated at 119, and is arranged so that its long arm 121 which engages a stud 123 on the diaphragm 109, moves the diaphragm and pin 111 to the right as the temperature decreases, and to the left as the temperature increases. Under very cold conditions, therefore, the amount of suction applied to head 101 is relatively small and primary choke 116 will only be opened a small amount when the engine is operating at a low speed. Under warmer conditions the pin 111 will be farther away from its seat 115, more suction will accordingly be applied to suction head 101 and the primary choke plate will be opened farther. A suction cylinder can be used in place of the diaphragm type suction head in FIG. 5, and conversely a diaphragm head can be used in place of the cylinder in the constructions of FIGS. 1 through 4, and 6.

FIG. 6 shows a separate temperature-responsive member used to control the variable limit stop for the amount of choking in a single barrel carburetor 129. In this construction a tapered limit slide 130 is attached via relatively rigid arm 128 to the long arm 123 of a .I- shaped bimetallic spring 125. The short arm 124 of said bimetallic spring 125 is secured to the housing of the suction cylinder 75. The bimetallic spring 125 is responsive to ambient temperature, its long arm 123 moving up as the temperature increases and down as the temperature decreases. Thus, the tapered limit slide 130 is moved up and down in response to the temperature. The general operation of the slide 130 in FIG. 6 is identical with that already described for slide 86 in FIG. 4.

In FIG. 6 the suction-operated rod 74 is linked through a slot 127 in a sector plate 126 fixed to the shaft 18 on which choke plate 16 is carried. The bimetallic spring 42 is here also directly secured to shaft 18 to directly actuate it, rotating it counterclockwise as seen in this figure, when the temperature drops.

Obviously many other modifications and variations of the present invention are possible in the light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

I claim:

1. A multibarrel carburetor connected to supply a fuel mixture to at least one intake manifold of an internal combustion engine, said carburetor having at least one primary induction passage and at least one larger secondary induction passage, a primary choke plate mounted in said primary induction passage for movement between opened and choking positions, a secondary choke plate mounted in said secondary induction passage for movement between opened and choking positions, a temperature-responsive member having actuating means connected to said choke plates to move them to choking positions in response to temperatures below a predetermined minimum and to open the choke plates in response to temperatures above said minimum, engine-operation-responsive means connected to urge the primary choke plate open during choked operation, a yieldable device in the connection of the actuating means with the primary choke plate to allow said primary choke plate to be moved toward opened position by said engine-operation-responsive means, the connection between the actuating means and the secondary choke plate being relatively nonyielding as compared with the primary choke plate connection to hold the secondary choke plate in less open position when the engine-operation-responsive means moves the primary choke plate toward open position.

2. The combination of claim 1 in which there is only one primary induction passage and its cross-sectional area is not more than about one-eighth of the total cross-sectional area of all induction passages.

3. The combination of claim 1 in which there is only one primary induction passage and its cross-sectional area is not more than about one-eighth of the total cross-sectional area of all secondary induction passages, the primary induction passage is connected to supply an unchoked combustion mixture having an airfuel ratio at least as high as about 14.5 to l, and the primary induction passage has aventuri-operated fuel jet connected to supply to that passage all idle fuel as well as fuel for all other operating modes.

4. A multibarrel carburetor as in claim 1 in which the engine-operation-responsive means includes an unsymmetrical pivot mounting for the primary choke plate to cause that plate to be urged toward open position by the movement of air into the carburetor.

5. A multibarrel carburetor as in claim 4 in which the engine-operation-responsive means includes an unsymmetrical pivot mounting for the secondary choke plate to cause that plate to be urged toward opened position by the movement of air into the carburetor.

I 6. A multibarrel carburetor as in claim 1 in which the engine-operation-responsive means includes 'a'suction the primary choke plate, to urge'said plate' 'toward open position inresponse to said suction.

7. A multibarrel carburetor as in claim 6 including a second suction head with a suction connection for the suction upstream of the throttle in the secondary induction passage, the second head being connected to the actuating means for the secondary choke plate to urge the last-mentioned plate toward open position in response to suction at the last-mentioned source.

8. The combination of claim 6 and further including limit means defining a maximum choke opening position for the suction head and temperature-responsive adjustment elements are connected to the limit means to gradually reduce that maximum as the choking temperature decreases.

9. The combination of claim 8 in which the temperatureresponsive adjustment elements are connected to modulate the suction in the suction head.

10. The combination of claim 8 in which the primary induction passage is connected to supply an unchoked combustion mixture having an air-fuel ratio at least as high as about 14.5 to l. I

11. The combination of claim 10 in which the primary induction passage has a venturi-operated fuel jet connected to supply to that passage all idle fuel as well as fuel for all other operating modes.

12. The combination of claim 10 in which the suction head has a maximum choke opening position, and temperature-responsive adjustment elements coact with the suction head to gradually reduce that maximum as the choking temperature decreases.

13. A multibarrel carburetor having at least one primary induction passage and at least one larger secondary induction passage, a primary choke plate mounted in said primary induction passage for movement between opened and choking positions, a secondary choke plate mounted in said secondary induction passage for movement between opened and choking positions, the temperature-responsive actuator being connected to both of said choke plates to move them to choking positions in response to temperatures below a predetermined minimum and to open the choke plates in response to temperatures above said minimum, a yieldable device in the connection between the temperature-responsive actuator and the primary choke plate toallow said primary choke plate to be moved toward opened position by said engine-operation-responsive means, the connection between the temperatureresponsive actuator and the secondary choke plate being relatively non-yielding as compared with the pri- 10 mary choke plate connection to hold the secondary choke plate in less open position when the engine-operation-responsive means moves the primary choke plate toward open positiomthe primary choke plate being unbalanced, means holding that plate oriented in an air intake for movement toward open position by air moving through that intake at speeds above idle,

engine-operation-responsive means with a suction connection for the suction downstream of the throttle, said engine-operation-responsive means being connected to the temperature responsive actuator to limit the cold closing of the plate when said suction is appreciable, and temperature-responsive elements connected to said engine-operation-responsive means to gradually lower the closing limit as the temperature diminishes, the connections from the temperature-responsive actuator and said engine-operation-responsive means to the choke plate including one-way connection means enabling the actuator and said enginge-operationresponsive means to move the plate but also permitting the plate to be independently opened wide by the airintake notwithstanding the actuator and said engine-operation-responsive means,

14. A carburetor having two barrels and an automatic choke system for both barrels, said system including an unbalanced choke valve in one barrel, means holding the valve oriented in an air intake for movement toward open position by air moving through that intake at speeds above idle, a temperatureresponsive actuator connected to the valve to move it to choking position when the temperature is below a predetermined minimum, engine-operation-responsive means with a suction connection for the suction downstream of the throttle, said engine-operation-responsive means being connected to the temperature-responsive actuator to limit the cold closing of the valve when said suction is appreciable, and temperature-responsive elements connected to said engineoperation-responsive means to gradually lower the closing limit as .the temperature diminishes, the connections from the temperature-responsive actuator and said engine-operationresponsive means to the choke valve including one-way connection means enabling the actuator and said engine-operation-responsive means to move the valve but also permitting the valve to be independently opened wide by the air-intake notwithstanding the actuator and said engine-operation-responsive means.

I I i I l: 

1. A multibarrel carburetor connected to supply a fuel mixture to at least one intake manifold of an internal combustion engine, said carburetor having at least one primary induction passage and at least one larger secondary induction passage, a primary choke plate mounted in said primary induction passage for movement between opened and choking positions, a secondary choke plate mounted in said secondary induction passage for movement between opened and choking positions, a temperature-responsive member having actuating means connected to said choke plates to move them to choking positions in response to temperatures below a predetermined minimum and to open the choke plates in response to temperatures above said minimum, engine-operation-responsive means connected to urge the primary choke plate open during choked operation, a yieldable device in the connection of the actuating means with the primary choke plate to allow said primary choke plate to be moved toward opened position by said engine-operation-responsive means, the connection between the actuating means and the secondary choke plate being relatively non-yielding as compared with the primary choke plate connection to hold the secondary choke plate in less open position when the engine-operation-responsive means moves the primary choke plate toward open position.
 2. The combination of claim 1 in which there is only one primary induction passage and its cross-sectional area is not more than about one-eighth of the total cross-sectional area of all induction passages.
 3. The combination of claim 1 in which there is only one primary induction passage and its cross-sectional area is not more than about one-eighth of the total cross-sectional area of all seCondary induction passages, the primary induction passage is connected to supply an unchoked combustion mixture having an air-fuel ratio at least as high as about 14.5 to 1, and the primary induction passage has a venturi-operated fuel jet connected to supply to that passage all idle fuel as well as fuel for all other operating modes.
 4. A multibarrel carburetor as in claim 1 in which the engine-operation-responsive means includes an unsymmetrical pivot mounting for the primary choke plate to cause that plate to be urged toward open position by the movement of air into the carburetor.
 5. A multibarrel carburetor as in claim 4 in which the engine-operation-responsive means includes an unsymmetrical pivot mounting for the secondary choke plate to cause that plate to be urged toward opened position by the movement of air into the carburetor.
 6. A multibarrel carburetor as in claim 1 in which the engine-operation-responsive means includes a suction head with a suction connection for the suction downstream of the throttle in the primary induction passage, the head being connected to the actuating means for the primary choke plate to urge said plate toward open position in response to said suction.
 7. A multibarrel carburetor as in claim 6 including a second suction head with a suction connection for the suction upstream of the throttle in the secondary induction passage, the second head being connected to the actuating means for the secondary choke plate to urge the last-mentioned plate toward open position in response to suction at the last-mentioned source.
 8. The combination of claim 6 and further including limit means defining a maximum choke opening position for the suction head and temperature-responsive adjustment elements are connected to the limit means to gradually reduce that maximum as the choking temperature decreases.
 9. The combination of claim 8 in which the temperature-responsive adjustment elements are connected to modulate the suction in the suction head.
 10. The combination of claim 8 in which the primary induction passage is connected to supply an unchoked combustion mixture having an air-fuel ratio at least as high as about 14.5 to
 1. 11. The combination of claim 10 in which the primary induction passage has a venturi-operated fuel jet connected to supply to that passage all idle fuel as well as fuel for all other operating modes.
 12. The combination of claim 10 in which the suction head has a maximum choke opening position, and temperature-responsive adjustment elements coact with the suction head to gradually reduce that maximum as the choking temperature decreases.
 13. A multibarrel carburetor having at least one primary induction passage and at least one larger secondary induction passage, a primary choke plate mounted in said primary induction passage for movement between opened and choking positions, a secondary choke plate mounted in said secondary induction passage for movement between opened and choking positions, a temperature-responsive actuator connected to both of said choke plates to move them to choking positions in response to temperatures below a predetermined minimum and to open the choke plates in response to temperatures above said minimum, a yieldable device in the connection between the temperature-responsive actuator and the primary choke plate to allow said primary choke plate to be moved toward opened position by said engine-operation-responsive means, the connection between the temperature-responsive actuator and the secondary choke plate being relatively non-yielding as compared with the primary choke plate connection to hold the secondary choke plate in less open position when the engine-operation-responsive means moves the primary choke plate toward open position, the primary choke plate being unbalanced, means holding that plate oriented in an air intake for movement toward open position by air moving through that intake at speeds above idle, engine-operation-responsive mEans with a suction connection for the suction downstream of the throttle, said engine-operation-responsive means being connected to the temperature responsive actuator to limit the cold closing of the plate when said suction is appreciable, and temperature-responsive elements connected to said engine-operation-responsive means to gradually lower the closing limit as the temperature diminishes, the connections from the temperature-responsive actuator and said engine-operation-responsive means to the choke plate including one-way connection means enabling the actuator and said enginge-operation-responsive means to move the plate but also permitting the plate to be independently opened wide by the air-intake notwithstanding the actuator and said engine-operation-responsive means.
 14. A carburetor having two barrels and an automatic choke system for both barrels, said system including an unbalanced choke valve in one barrel, means holding the valve oriented in an air intake for movement toward open position by air moving through that intake at speeds above idle, a temperature-responsive actuator connected to the valve to move it to choking position when the temperature is below a predetermined minimum, engine-operation-responsive means with a suction connection for the suction downstream of the throttle, said engine-operation-responsive means being connected to the temperature-responsive actuator to limit the cold closing of the valve when said suction is appreciable, and temperature-responsive elements connected to said engine-operation-responsive means to gradually lower the closing limit as the temperature diminishes, the connections from the temperature-responsive actuator and said engine-operation-responsive means to the choke valve including one-way connection means enabling the actuator and said engine-operation-responsive means to move the valve but also permitting the valve to be independently opened wide by the air-intake notwithstanding the actuator and said engine-operation-responsive means. 